A voltage adjusting apparatus includes a pulse width modulation (PWM) controller, a switch module, and a feedback module. The PWM controller outputs control signals. The switch module receives the control signals, and outputs working voltages accordingly. The feedback module includes a jumper, a first resistor, a second resistor, and a third resistor. If the first terminal and the second terminal of the jumper are electrically coupled together, the third resistor is cut off from the feedback module by the jumper, the first resistor and the second resistor are electrically coupled in the feedback module, and the switch module outputs a first working voltage accordingly. If the second terminal and the third terminal of the jumper are electrically coupled together, the first resistor, the second resistor, and the third resistor are all electrically coupled in the feedback module, the switch module outputs a second working voltage accordingly.